In recent decades, polymeric microporous materials have been a topic of considerable interest for industrial and academic researchers because of their promising application in gas separation membrane, sorption resins, chromatographic materials and hydrogen storage media. Among polymeric microporous materials, a new class of ladder-type polydibenzodioxanes having sites of contortion, referred to as polymers of intrinsic microporosity (PIMs) by the inventors Budd et al. and McKeown et al. (Budd 2004a; Budd 2004b; Budd 2005a; Budd 2005b; McKeown 2005a) are recently attracting much attention. The rigid special structure of the main chain provides significant advantages, such as good processibility, a broader range of physical properties, potential for introducing functionality and high permeability combined with a moderate selectivity for membrane gas separation.
PIM-type materials are characterized by having repeat units of dibenzodioxane-based ladder-type structures combined with sites of contortion, which may be those having spiro-centers or severe steric hindrance. The chain structures of PIMs prevent dense chain packing, causing considerably large accessible surface areas and high gas permeability. Because of their distinctive structures, only a few tetraphenol monomers and tetrahalogenated monomers have been suitable for polymerization to provide high molecular weight PIM homopolymers and copolymers (McKeown 2005b; Du 2009a; Du 2008a; Du 2009b). It is desirable to expand the structural variety of PIM-type materials that contain the inherently stiff dibenzodioxane ladder structure and contorted center. In previous work, two approaches were pursued to access structurally new PIM materials: (1) the design of tetrafluoro monomers containing sulfone electron-withdrawing groups; and (2) post-polymerization modification of the PIM nitrile group by controlled hydrolysis.
PIM-1 is the most well-known and reported PIM-type materials for perhaps several reasons: (1) it has among the simplest structures; (2) it is made from commercially available monomers; (3) it is obtained in high molecular weight; and (4) it has reasonably good mechanical properties. As shown in Scheme 1, the PIM-1 repeat unit contains two nitrile groups, which is an appropriate substrate for testing the present approach for post-modification.

In previous work, a practical and controlled hydrolysis reaction of the nitrile groups in PIM-1 was reported, which resulted in structurally new PIM materials containing carboxylic groups. The gas permeation properties of the carboxylated PIMs were reported and discussed with respect to the degree of hydrolysis (Du 2009c).
Besides the nitrile hydrolysis reaction, the [2+3] cycloaddition reaction between a nitrile and azide is a route to tetrazoles. This type of reaction has also been referred to as “click chemistry” when accomplished in the presence of specific catalysts, on account of its rapid and high yield, and is a representative of a group of 1,3-polar cycloadditions, (a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) (Kolb 2001; Huisgen 1967). It has been successfully carried out by heating (80-120° C.) a mixture of the neat starting compounds (Demko 2002a; Demko 2002b) or in solvents such as DMSO or DMF and even in aqueous media (Demko 2001). The reaction is catalyzed by protic acids such as ammonium salts and acetic acid or Lewis acids, such as SnCl2 or ZnCl2. The mechanism of the Zn(II)- and Al(III)-catalyzed reaction was recently studied theoretically and most likely involves coordination of the metal ion to a nitrile molecule (Himo 2003). Similar to the ZnCl2 catalyzed Click reactions between azide and nitrile groups to yield low molecular weight tetrazole compounds (Binder 2007), post-polymerization modification reactions for attaching tetrazoles onto nitrile-containing polymers has become somewhat of a re-discovery (Tsarevsky 2004) with several apparent advantages which include (1) quantitative yields, (2) a high tolerance for the presence of other functional groups, (3) an insensitivity of the reaction to solvents, irrespective of their protic/aprotic or polar/non-polar character, and (4) reactions at various types of interfaces, such as solid/liquid, liquid/liquid, or even solid/solid interfaces. Until now, relatively little work on the post-polymerization [2+3] cycloaddition modification of nitrile-containing polymers has been reported.
Further, during the last decade, ionic liquids, which are organic salts with a melting point lower than 100° C. (Earle 2002), have attracted considerable interest because of their excellent chemical stability, non-flammability, and negligible volatility (Wasserscheid 2000). In the last five year, ionic liquids have been explored as ideal media candidates called promising “green materials” to replace volatile organic compounds (VOCs) in gas scrubbing, separations, and storage/delivery applications. Especially, these materials have great utility in applications involving CO2 separations, due to the high solubility of CO2 in ionic liquids (Blanchard 1999; Tang 2005a; Plechkova 2008). Permeabilities, solubilities, and diffusivities of CO2 in ionic liquids are usually measured by using a supported ionic liquid membrane (SILM) which have already shown very promising performance for CO2 (Scovazzo 2004; Morgan 2005; Gan 2006; Ferguson 2007). However, one of the major drawbacks associated with SILMs is that the ionic liquid is held in the pores of the support via relatively weak capillary forces. If the transmembrane pressure differential exceeds those forces, the ionic liquid will be pushed through the support, destroying the membranes' selectivity (Bara 2007). Thus, SILMs are usually only tested at pressure differentials of about 0.2 atm. Nanoporous supports have been used to successfully overcome these limitations, and SILMs made using these supports have been reported to be stable at pressures up to 7 atm (Gan 2006).
Polymeric forms of ionic liquids is another approach providing exceptional properties, such as chemical stability and excellent CO2 capture properties (Tang 2005b; Bara 2007). Tang and his coworkers found that solid polymerized ionic liquids absorb CO2 with a higher absorption capacity and at a much faster absorption rate than room temperature ionic liquids (Tang 2005a; Tang 2005c). But, the permeabilities of all these materials reported as polymerized ionic liquids are very low due to the nature of the polymer main chain. In addition, most of the previously reported pure polymerized ionic liquids were too brittle to make mechanically stable membranes (Hu 2006).
In general, PIM-type materials are characterized as having very high gas permeability and moderate gas-pair selectivity. However, there still remains a need for devising new PIM-type materials having improved selectivity or other properties.